Well, (Jahazi) the 50Hz is clearly a/c line noise, maybe from the within the measurement setup, maybe from lighting/etc., maybe both. As for the really low stuff, it is kind of unlikely you have a setup that can actually measure below 20Hz, but feel free to correct me if you do.

DrDayna, considering the lowest "natural" note is 32 Hz, what are you listening to? I might want to have something like that for a reference as I don't care for heavy organ. If it is electronic though, I'll pass.

B0 on a 5-string bass or a normal double bass is 31Hz.

That'd also imply an A0 note, which IIRC is ~28Hz.

Its rare to see anything tuned that low, as most systems won't reproduce it anyway.
Some of the larger pianos would do it (and probably lower, given enough strings).

DrDayna, considering the lowest "natural" note is 32 Hz, what are you listening to? I might want to have something like that for a reference as I don't care for heavy organ. If it is electronic though, I'll pass.

Electronic.

Edit: But, should we consider this "un-natural"? Just because some musicians carve their instruments out of computers instead of wood doesn't mean we shouldn't evolve our thinking about music. Good thing we've evolved at least as much as we have, if we had this discussion before the invention of musical instruments, some of you might be making the argument that we don't need a speaker that plays any lower than a person could sing.

Then someone decided it would be cool to hollow out a tree trunk and beat on it with a stick...and ever since then, we've been chasing that feeling.

This is what one of my earlier comments hinted at, where a lot of people form opinions about what's necessary based on prejudice about music and artistry, what's real, what's fake, this is music, this is not, yadda yadda yadda.

If you're confined by your own musical taste, it'd probably be best to refrain from giving musical reproduction advice, unless the recipient of the advice is forewarned about the absolutely subjective nature of the advice.

tvrgeek
I don’t know what the level of ~ -115dbu really means (what is your 0dbu?) but I guess that your office is really quiet, at least on low frequencies. For this, you’d better average more than 10x measurements to see the room modes.
The more noisy a space is, the more energy exists to excite the room modes and the less averaging is required.
e.g. The noise of a heavy vehicle passing through a nearby street, provides a broadband acoustic energy with changing frequency .
Room modes are strongly excited and remain excited at their set frequencies for some time, so that even x2 or x3 averaging will reveal them.

George
.

__________________["Second Law is a bitch." - SY] ["BTY my shop's large door is 14 feet wide so I can get my ego in each morning. Some evenings it can leave via the mail slot". -Ed Simon]

DrDayna, considering the lowest "natural" note is 32 Hz, what are you listening to? I might want to have something like that for a reference as I don't care for heavy organ. If it is electronic though, I'll pass.

I am not too far from a highway, and my sub-30 Hz noise is very high too. You don't notice it during the day, but if you sit out at night, the source becomes very clear.

I had this same problem. I used to live near a major interstate in Northern California. I also had a sub-30hz noise problem that could be best illustrated by setting a glass of water on any surface in that apartment. You could easily see the ripples in the water, even if you could not hear the traffic noise.

I am not suggesting electronic is not music, just not "natural Western scale" musical notes. Music is what the artist offers. We like it or not. If an artist is trying to woo an Elephant, than 10Hz is probably quite necessary. Listening to anything on a CD, nope. I also know a bit on how amps work, and understanding both the input DC blocking networks, feedback methods and/or DC servo, you are not producing 10 Hz anyway unless you built a very special amp to do so. No one here is arguing that a 30 Hz fundamental is not unreasonable. So understanding the roll-off of the woofer, what is necessary to produce 30 Hz? I use sealed subs with F3 of 25Hz and 25 Hz second order HP filters, so a 30 fundamental is a bit weak on my system considering I have a third order HP at 25, plus or minus the room. One of these days I may add a peaking filter (LT) to give the 30 to 35 that little extra touch. I am not sure the neighborhood would appreciate it though.

Watching my analyzer to Blackwood Night. Strong kick drum at about 50 Hz, It is showing significant energy to 10 Hz. Sub OFF. Tain't nuttin there but artifacts of how DSP works folks! My amp won't produce it, and my mic won't pick it up, and preamp won't pass it to the computer. Don't be fooled by a squiggly line on a computer if you don't understand what it is really measuring and calculating. FFTs only tell you what the calculation says, not the truth.

tvrgeek
I don’t know what the level of ~ -115dbu really means (what is your 0dbu?) but I guess that your office is really quiet, at least on low frequencies. For this, you’d better average more than 10x measurements to see the room modes.
The more noisy a space is, the more energy exists to excite the room modes and the less averaging is required.
e.g. The noise of a heavy vehicle passing through a nearby street, provides a broadband acoustic energy with changing frequency .
Room modes are strongly excited and remain excited at their set frequencies for some time, so that even x2 or x3 averaging will reveal them.

George
.

Fairly quite office. -80 maybe. The analyzer was peak hold of many minutes of 5X averaging. Scale is only relevant, not calibrated. Could be just not noisy enough to see any modes excited above ambient. I keep an old analog sweep generator for room testing. Great for finding things that don't behave. Back of china closet, center speaker, a spring bail in one window, and being sure the felt pads under all the paintings are doing their job. Also fun to see how dramatic the modes are as you walk around.
I may try low levels of noise to see what threshold starts to show measurable issues. If your idea is correct, I should see them rise out of the background.

I don't know what a -115 dB room would sound like. I believe the blood in your ears is considerably louder than that. You can hear it sitting in a quite mountain pass in the snow or in a cave quite clearly.

My methods were questioned. Seems to me that I'm the only one who is telling how they measure! Is this why I am under charge? My graph was meant to be a teaser for this discussion, not a "truth"

I quickly took new measurements with three different programs and this time the microhone is Microsoft LivCamHD. Yes, it has an amazing mic! I didn't even try to adjust levels.

Audacity graph is comparable to Zoom measurement, but location is different and this time the mic was lying on sofa (different place) Same position here in every measurement.

REW was set to C weighting.

Yes, i Can hear the ambient noise very well! The PC makes noise and air criculation system is on. Cars and trains are 600m away. Nobody was walking or talking in the house.

Can you set me free now? What about other peoples methods? I am not a scientist and I'll not spend money on a specific calibrated measuring microphone. I don't get paid for this and I don't own stocks of any AV company.

About measured responses and music - commercially produced music hardly ever contains signals <30Hz (noise at level of -70dB and less though) The speakers have trouble trying to put out those fQ and they have significant distortion then. Some of distortion is 1/2 of main Fq. Low sounds also excite the air, window panes, curtains, tables, paintings on the wall etc. They make resonances too. All this contributes to measurements done at listening site. This shoud be a well known fact, only the level of this noise is vague without some measurements of it! Every measurement gives slightly different results, because there are so many variables.

Have you ever heard of anechoid chambers? They have ambient noise too. You can't get away from it but you must know where and how much of it is.

My methods were questioned. Seems to me that I'm the only one who is telling how they measure! Is this why I am under charge? My graph was meant to be a teaser for this discussion, not a "truth"

Sorry, I meant to imply that probably none of the measurements being posted were valid below 20Hz (if that), and also that noise in the measurement system needs to be measured and considered. Not only your measurements.